Human p140(trk) and p75(NGFR) were transfected separately into 3T3 cells. Nerve growth factor stimulates calcium uptake into both transfectants but not into untransfected 3T3 cells. p140(trk) cells were stimulated maximally by 25 ng/ml; 100 ng/ml was submaximal for p75(NGFR) cells. K-252a inhibits the effect of NGF on p140(trk) cells but not on p75(NGFR) cells; brain-derived neurotrophic factor stimulates calcium uptake in p75(NGFR) cells but not in p140(trk) cells. The data suggest that both nerve growth factor receptors could be involved in the nerve growth factor-mediated actions of calcium on its target cells: neuronal survival, neuronal protection, and synaptic plasticity.